I'm sure it's been talked about before, but THE most important thing for me is that they do NOT do Batman's first encounter with the Joker.
I've seen that story twice on screen now. I'm good. One of the best parts about the characters' relationship in the comics is its longevity. The fact that it's a twisted dance that just keeps going and going.
I want that explored. What was teased at the end of The Dark Knight but couldn't be done for obvious reasons.
Basically. Give me a Batman and Joker who are already familiar with each other please
And Harley Quinn.